This invention relates to the field of check valves, and, in particular, addresses the problems of banging or slamming of the valve disk against the valve seat, due to sudden reversals of flow in the line.
Check valves, i.e. valves which allow fluid to flow through the valve in only one direction, have been known for a long time. The typical check valve includes a disk (also known as a "clapper", or simply a "valve element", among other names) which is biased by a spring means, or by gravity, to rest against a seat. The disk is forced away from the seat by the pressure of an incoming fluid. Movement of the disk away from the seat opens a path for fluid to flow through the valve.
When the direction of flow of fluid in the line is suddenly reversed, the valve described above tends to close immediately. The disk is immediately forced against the seat, by the combined action of the spring means, or gravity, and the line fluid itself. When the fluid line is connected to a reciprocating compressor which, due to defects in the compressor's discharge valves, draws some fluid back on its return stroke, the slamming of the disk of the check valve can be especially severe. Such compressors typically operate at rates of the order of 350 strokes per minute, and the valve disk therefore tends to move with these strokes, slamming repeatedly against its seat. This slamming, or "chatter", can eventually damage or destroy the valve.
Because of the slamming problem, some check valves have been limited to use with liquids, whose pressures are less variable than those of a gas. Such valves could occasionally be used with gases, but only when the gas flow was expected to be fairly uniform. But in many other applications, such as with the compressor mentioned above, the changes in the direction of gas flow may be large and frequent, and the problem of slamming must be addressed.
Many solutions have been proposed, in the prior art, for the problem of the slamming of the valve disk. One solution is to provide some kind of damping means for cushioning the motion of the disk, as it moves towards its seat. Such a damping means is shown in U.S. Pat. No. 4,330,006, wherein a fluid cushions the return of the disk, and flows out of the valve, relatively slowly, through the clearances between the valve components. Another example of a fluid damping device is shown in U.S. Pat. No. 3,086,550, which provides an air chamber to cushion the valve disk.
Other examples of patents which disclose the use of a fluid chamber for damping the movement of a valve disk include U.S. Pat. Nos. 3,857,408, 4,315,524, and 3,422,843. Other patents show structures which damp the movement of the disk by mechanical linkages, and the like. Examples include U.S. Pat. Nos. 4,340,085 and 3,109,450.
In check valves which are damped by a fluid chamber, the chamber is generally defined by the valve disk and valve seat, or by a valve and disk and a central member or wall adjacent the seat. The chamber is filled with fluid as the disk is moved away from the seat, and the disk therefore pushes against the fluid as it returns towards the seat. The fluid which is pushed out of the chamber therefore is forced through the clearances between the disk and its surrounding structure, to the outside.
Check valves which are damped by a fluid are preferred over those which are damped by mechanical means. Fluid-damped valves require fewer components, and therefore are easier and less expensive to build, and are likely to be more reliable in operation. The fluid to be used for damping purposes can be easily "borrowed" from the fluid flowing in the line.
The problem with fluid-damped check valves is the irregularity of the path through which the damping fluid escapes. It is difficult, if not impossible, to maintain a precise tolerance between the disk and the adjacent components. During the life of the valve, the constant flow of fluid through the clearances between the valve components causes the size of these clearances to change, and therefore changes the rate of damping of the movement of the disk. It is important to provide a controlled rate of flow of the damping fluid out of the valve.
The present invention provides a solution to the problem described above. The invention includes a check valve wherein the movement of the valve disk is damped by a fluid, and wherein the fluid flows out of the valve at a controlled rate, when the disk is moving towards its seat. The disk can therefore return to the seat only if the pressure in the line remains low for an extended period of time. If the disk does return to the seat, it will do so without slamming.